1. Field of the Invention
The present invention relates to a tandem type printing system including serially disposed printing devices.
2. Related Art
There have been proposed tandem type printing systems that include a pair of printing devices serially disposed for forming images on both surfaces of a web. That is, a first printing device at a front stage performs printing on a front surface of a web. The web discharged outside the first printing device is turned upside down by an inversion device, and is supplied to a second printing device at a post stage, which performs printing on a rear surface of the web.
This type of printing system uses as a web a continuous recording sheet with feed holes formed along its longitudinal edges. Systems that can use a web without feed holes are becoming popular. However, when a web with no feed holes is used, it can be difficult to align the position of the rear-surface image with the position of the front-surface image.
This is particularly a problem when the first printing device is a type of printing device that forms images using electrophotographic techniques. That is, heat generated to thermally fix the toner image transferred onto the web in place can thermally shrink the web from its initial condition. As a result, the web can be shorter when fed to the second printing device. Accordingly, because the page length when the front surface is printed on differs from the page length when the rear surface is printed on, the position of the front-surface image will not match the position of the rear-surface image, causing positional deviation between the front-surface image and the rear-surface image.
In view of foregoing, there has been proposed a following control method. That is, the first printing device forms a position-alignment mark on a leading edge of each page on the web. Then second printing device measures the distance or detection timing of the position-alignment marks. Controlling the web transport speed based on this measuring result can prevent such a positional deviation, so that the rear-surface images are formed on the position corresponding to the front-surface images.
However, even if the web transport speed is controlled in this manner, as the pages have the longer length, adjusting frequency of the web transport speed decreases, so that the positional alignment between the front-surface image and the rear-surface image becomes less precise. In other words, when the page has a longer length, the positional deviation between the front and rear surface images occurs more likely.
In the view of foregoing, it is an object of the present invention to overcome the above problems, and also to provide tandem type printing system capable of realizing precise positional alignment between front-surface images and rear-surface images on a web even if pages have an increased length.
In order to overcome the above and other objects, according to the present invention, there is provided a tandem type printing system including a first print device, a second print device, and a communication means for communicating with first print device and the second print device. The first print device includes a first printing means for forming a first-surface image on a first surface of a web. The second print device includes a second printing means for forming a second-surface image on a second surface of the web, a transport means for transporting the web, and a control means for controlling the transport means. At least the first print device includes a mark forming means for forming position-alignment marks on predetermined positions on the first surface of the web. The communication means transfers mark information on the position-alignment marks formed on the first surface to the control means of the second print device. At least the second print device includes a detection means for detecting the position-alignment marks formed on the first surface. The control means controls, based on the mark information and detection results from the detection means, the transport means to transport the web so as to match a positional phase of the second-surface image with a positional phase of the first-surface image.
There is also provided a tandem type printing system including a first print device and a second print device. The first print device includes a first printing means for forming a first-surface image on a first surface of a web. The second print device includes a second printing means for forming a second-surface image on a second surface of the web, a transport means for transporting the web, and a control means for controlling the transport means. At least the first print device includes a mark forming means for forming position-alignment marks on predetermined positions on the first surface of the web. The mark forming means forms the position-alignment marks on a plurality of locations in each page of the web. At least the second print device includes a detection means for detecting the position-alignment marks formed on the first surface. The control means controls, based on detection results from the detection means, the transport means to transport the web so as to match a positional phase of the second-surface image with a positional phase of the first-surface image.